I believe the confusion in these posts comes from the context and connection between masks and the vaccine. It sounds like people are equating vaccine use and reducing mask use. But, they’re not related that way. The vaccine part of these doesn’t matter. Once no longer needed because spread is low, I wouldn’t expect many people to wear a mask.
This is the better question. On one side of the equation is infection spread and impact, on the other is mitigation efforts to reduce spread. The vaccine is just one way to reduce spread. Masks are a way to reduce spread. As long as spread and impact are still high enough, all reduction techniques will be used.
Wide vaccine use should create a dramatic drop in spread. It should also reduce the impact. Once that happens, we'll see masks and other mitigation’s relaxed. Not because of the vaccine itself, but because of the reduction.
If we had reduced spread other ways, we could reduce mitigations then too. We didn’t need the vaccine to do it. Ignoring vaccine development, since most of us aren’t part of that, the vaccine is just the easiest way to reduce spread.
I don’t know what the correct level is, but it’s WAY below the current level today.